The present invention relates to an improved burner and burner method used, for example, in the production of asphalt and, in particular, to a versatile burner of simplified construction which promotes more complete mixing of fuel and air over a wide range of operating conditions and which utilizes a unique combination of primary and secondary fuel injection when the burner uses gaseous fuel as well as liquid propane and butane.
Combination fuel aggregate dryer burners are disclosed, for example, in U.S. Pat. Nos. 4,559,009 and 4,298,337 as discussed in commonly assigned U.S. Pat. No. 5,259,755, which discussion is incorporated by reference herein. Many other burners are also currently available or known for the combustion of gas, liquid fuel and combinations thereof as shown, for example, in U.S. Pat. Nos. 3,163,203; 3,217,779; 3,391,981; 4,441,879; 4,451,230; 4,717,332; 4,859,173; and 5,009,174.
It is a goal of all these burners to provide a compact and efficient combustion burner, large turn-down ratio, flame stability, ability to switch between fuels, dependable operation and economical manufacture. The combustion burner shown, for example, in the above-mentioned U.S. Pat. No. 3,163,203, swirls a liquid fuel/air mixture through vane slots into a combustion chamber and the gaseous fuel is passed through axially-disposed nozzles where it is then mixed with the swirling air.
Due to the unique problems and operating conditions associated with the production of asphalt, however, these known burners and others constructed specifically for the asphalt production operation are unduly complicated in their constructional features and do not perform satisfactorily under all conditions. They also lack other advantages and features such as the ability to provide increased turn down at low fire and extremely stable and intense combustion throughout the burner's firing range in a simple way so as to reduce emissions without, for instance, the need for a compressed air source.
As discussed in U.S. Pat. No. 5,259,755, we found that the known burners used in the asphalt industry do not satisfactorily enhance and protect the base of a flame recirculation zone under oil flame. In addition, whereas the prior burners used in asphalt production are known for use with refractory burner block or for use in a refractory-less application, these burners do not provide a satisfactory arrangement for use both with and without refractory burning block depending on which is required based on the desired use temperature. That is, thermal oxidizers and other applications that these known burners could be used for require a higher operating temperature and also might require a refractory tile. Although the combination burner described in U.S. Pat. No. 5,259,755 constitutes a substantial improvement over previously known burners, we found that in the typical dusty environments encountered in asphalt production resulted in incomplete combustion under certain operating conditions. This, in turn, results in too much combustion occurring outside the combustion chamber with leftover combustibles.
An object of the present invention is, therefore, to provide a new, even more versatile burner and burning method which constitutes an improvement over the burner described in U.S. Pat. No. 5,259,755 and which provides more complete mixing of fuel and air over a wider range of operating conditions, particularly in the production of asphalt, in contrast with the known burners wherein only a portion of the air, about one-third of the total volume, has the fuel injected thereinto.
Another object of the present invention is to provide more complete mixing of the fuel and air to obtain more rapid combustion or combustion intensity (i.e., the BTU output per hour divided by the combustion space) for reducing the overall burner size and lowering CO emissions in a given combustion space before the flame leaves the combustion zone of the dryer.
Yet a further object of the present invention is to provide a burner which encourages internal recirculation through swirl to promote more rapid and complete combustion and to achieve NO.sub.x levels of lowest possible amount with very high combustion intensity and low O.sub.2 levels.
Still a further object of the present invention is to provide a burner which produces a lower noise level and which will run smoother with less resonance in the duct work and drums due to a more stable flame with less pulsing.
A further object of the present invention is to provide a burner which requires lower horsepower than previous burners of the same BTU capacity.
A still further object of the present invention is to provide a burner which can be adapted to industrial and high temperature applications where optional refractory burner tile is used for use in refractory lined combustion chambers such as incinerators.
Still another object of the present invention is the provision of a burner having a wider flame than previously obtained which is particularly advantageous with the use of large diameter drums in the production of asphalt.
These objects have been achieved in accordance with the present invention by the provision of a total air burner in which all the air passes through adjustable spin vanes and the fuel is injected into the entire airstream, rather than separating combustion air into two different streams with the fuel injected into only a portion thereof.
Another feature of the present invention is that it produces a wider flame than conventional asphalt burners with the same firing lengths at 50% and 100% firing. This has an advantage over narrower and longer flames of known burners for customers that have large diameter drums.
As a result of the foregoing, a more versatile burner has been produced which uses a burning method usable over a wider range of operating conditions than previously available burners were able to achieve due to its simplified constructional principles using a unique combination of primary and secondary fuel injection when using gaseous and liquid propane and butane to achieve complete combustion and flame stability. Because the burner in accordance with the present invention is inserted only slightly into the drum, it can run with a cooler aggregate dryer breach plate. Furthermore, the burner in accordance with the present invention, like the burner described in U.S. Pat. No. 5,259,755, uses less horsepower than open fired burners of similar BTU capacity and can be used also in industrial and high temperature applications with refractory burner tile in refractory-lined combustion chambers such as incinerators.